Diagnostic magnetometry using superparamagnetic particles

ABSTRACT

The use of superparamagnetic particles and of paramagnetic materials (such as lanthanide chelates) as contrast agents in magnetometric analysis, especially imaging, and in particular structural and functional, diagnosis or imaging is described.

This invention relates to the use of paramagnetic and superparamagneticsubstances as enhancing agents for diagnostic magnetometery, especiallyusing a superconducting quantum interference device magnetometer (aSQUID) and preferably as imaging contrast agents in magnetometricimaging, in particular SQUID imaging.

In 1963 James Zimmerman, a researcher at Ford Motor Company, observedthat when a non-superconducting boundary is present in a superconductingloop a special effect is created. This effect is extremely sensitive tomagnetic flux and based on Zimmerman's work the very highly sensitiveSQUID magnetometers have been developed and are now availablecommercially from companies such as Biomagnetic Technologies Inc of SanDiego, Calif. and Siemens AG of West Germany.

SQUID magnetometers generally comprise a superconducting pick up coilsystem and a detector system (the SQUID) which itself comprises one ortwo Josephson junctions inserted into a loop of superconducting wire.The magnetic flux within such loops is quantized and changes in themagnetic field experienced by the pick up coils cause an immediate andmeasurable change in the current flowing through the detector. The SQUIDmagnetometers available include both single and multichannel devices,the latter being capable of detecting magnetic fields at plurality oflocations simultaneously.

SQUID magnetometers are capable of measuring magnetic fields as low as10⁻¹⁴ Tesla, one ten billionth the earth's magnetic field, and thus areable to detect magnetic fields generated by biological activity such asfor example the fields of the order of 10⁻¹³ T which are induced by theelectrical activity of the brain. The sources of nerve signals can thusbe traced to within a few millimeters.

SQUIDS and their use in the study of biomagnetism are discussed forexample by Wolsky et al. Scientific American, February 1989, pages60-69, Philo et al. Rev. Sci. Instrum. 48:1529-1536 (1977), Cohen IEEETrans. Mag. MAG-11(2):694-700 (1975), Farrell et al. Applied PhysicsCommunications 1(1):1-7 (1981), Farrell et al. IEEE Trans. Mag.16:818-823 (1980), and Brittenham et al. N. Eng. J. Med.307(27):1671-1675 (1982). The SQUID may be designed to detect themagnetic field or, may be of the gradiometer type and which severaldesigns exist.

Indeed the development of biomagnetic analysis has been closely linkedto the development of SQUID detectors since conventional magnetometers,such as Bartington detectors or Hall-probe gaussmeters, are severalorders of magnitude less sensitive to magnetic field changes.

In the study of biomagnetism, or more specifically, the in vivemeasurement of magnetic susceptibility, the sensitivity of SQUIDS hasbeen such that the researchers' concentration has primarily been onthree areas--the detection of electrical activity within body tissues bydetection of the accompanying magnetic field changes, the in vivedetermination of iron concentrations in the liver in order to detectiron overload or iron deficiency there, and the detection offerromagnetic particle contamination in the lungs.

In the first two cases, the magnetic fields detected by the SQUIDS arisefrom normal or stimulated nerve activity or from the normal presence of(paramagnetic) iron in the liver. In the third case, particlecontamination is by magnetic particles, e.g. of magnetite, and theirmagnetic effect is first maximized by placing the subject in a magneticfield. The resultant magnetization is detectable by a SQUID for theperiod of months over which it decays.

Due to the extreme sensitivity of the SQUID technology enabling thebody's electrical activity to be monitored, there has been littleemphasis on the use of SQUIDS for the generation of images, inparticular two or three dimensional images, of the body's internalphysical structure rather than electrical activity images.

For such localisation to be effective it must be possible to generatemagnetic susceptibility differences between different body tissues,organs and ducts and rather than doing this by provoking electricalactivity or by relying on natural aggregations of non-diamagneticmaterial we now propose the administration in diagnostic magnetometery,especially magnetometric imaging, of enhancing agents comprisingparamagnetic or superparamagnetic substances. SQUIDS are sufficientlysensitive to detect the changes in local magnetic susceptibility wheresuch agents distribute within the body so enabling contrast enhancedmagnetometric signals or images to be generated, for example for use indiagnostics.

Thus viewed from one aspect the present invention provides the use of aphysiologically tolerable paramagnetic or superparamagnetic material,and in particular paramagnetic lanthanide metal ion chelates and free ormatrix borne superparamagnetic particles, for the manufacture of adiagnostic agent for use in magnetometric analysis, preferably bymagnetrometic imaging, of the human or non-human, preferably mammalian,animal body.

Viewed from a further aspect, the invention also provides a method ofdiagnosis of the human or non-human animal body which method comprisesadministering to said body a physiologically tolerable paramagnetic orsuperparamagnetic material and generating a magnetometric signal of atleast a part of said body into which said material distributes,preferably but not essentially using a SQUID based system, especially amultichannel SQUID.

Viewed from another aspect the invention also provides a method ofgenerating a magnetometric image of the human or non-human animal bodywhich method comprises administering to said body a physiologicallytolerable paramagnetic or superparamagnetic material and generating amagnetometric image of at least a part of said body into which saidmaterial distributes, in particular generating a two or threedimensional structural image and preferably but not essentially using aSQUID based imaging device, especially a multichannel SQUID imager.

Viewed from a still further aspect, the invention also provides aprocess for detecting variations in magnetic susceptibility within ahuman or non-human animal body which process comprises administering tosaid body a physiologically tolerable paramagnetic or superparamagneticmaterial, and with a magnetometer continuously or repeatedly monitoringthe magnetic susceptibility of at least a part of said body into whichsaid material distributes, for example to generate magnetometric signalsor preferably images of variations or abnormalities in blood flow, or tomonitor the location and aggregation of these materials within regionsof the body, for example the arrival and accumulation of tissue- ororgan- targeting substances at the targeted region, e.g. a tumour, thereticuloendothelial system, etc. and optionally to generate amagnetometric image thereof.

Viewed from another aspect the invention also provides the use of aphysiologically tolerable paramagnetic or superparamagnetic material,and in particular paramagnetic lanthanide metal ion chelates and free ormatrix borne superparamagnetic particles, for the manufacture of adiagnostic composition for use in the process according to theinvention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 represents a multichannel SQUID analysis without any sample.

FIG. 2 represents a multichannel SQUID analysis using starchmicrospheres according to Schroder et al.

FIG. 3 represents a multichannel SQUID analysis using Gd-DTPA BMAprepared according to Quay.

DETAILED DESCRIPTION OF THE INVENTION

The method and process of the invention may be performed using anymagnetometric technique but are particularly suited to the use of SQUIDbased magnetometers. Thus the process of the invention for example maybe performed using single channel SQUIDS but would preferably beperformed using a multichannel SQUID system.

The paramagnetic or superparamagnetic substances used according to theinvention and for convenience referred to herein as magnetometricdiagnostic agents may, in view of the sensitivity of SQUIDmagnetometers, be any such material which is biotolerable in the dosagesand with the administration form and route that is used. There is ofcourse no necessity to pre-magnetize the subject followingadministration of the diagnostic agent before transferring the subjectto the magnetometer location (generally a region of homogeneous magneticfield or a magnetically shielded room). However, the contrast agent maybe pre-magnetised before administration and it may also be advantageousto pretreat the magnetic substance to prevent conglomeration thusobtaining a maximum field for a given concentration of subtance.

The process and method of the invention can be performed with or withoutthe imposition of an external magnetic field (besides or in place of theearth's natural magnetic field that is). Imposed fields can be variant,e.g. pulsed, or invariant. Where the contrast agent used issuperparamagnetic the method and particularly the process of theinvention may advantageously be performed with no pre-magnetization andwith no imposed magnetic field or with only a static imposed magneticfield. However where the contrast agent used is paramagnetic rather thansuperparamagnetic, the magnetometric investigation according to theinvention will preferably be performed with the subject exposed to animposed pulsed or invariant magnetic field, at least in the region ofinterest. This field can be relatively localized in effect and can be aslow as 10⁻⁴ T but in one convenient embodiment may be the primary field,generally of up to 10¹ T, generated by the primary coils of a magneticresonance imager. Where the contrast agent is superparamagnetic anexternal field can be but need not be applied.

Particularly preferred diagnostic agents will include those which haverelatively high magnetic susceptibilities, in particularsuperparamagnetic particles and substances containing high spinparamagnetic metal species, especially high spin transition metal andlanthanide ions, in particular ions of Mn, Fe, Dy, Gd, Eu, Tb, Tm, Yb,Er and Ho, most particularly Dy(III). A wide variety of such materialshave been proposed for use as contrast agents in magnetic resonanceimaging (MRI), and MRI contrast agents will in general also be suitablefor use as magnetometric diagnostic (MD) agents, including magnetometricimaging (MI), contrast agents.

Thus particular mention may be made of the superparamagnetic contrastagents already proposed for use as MRI contrast agents by for exampleJacobsen et al. in U.S. Pat. No. 4,863,716, by Klaveness et al. inWO-A-89/11873, by Schroder et al. in WO-A-85/02772, by Groman inWO-A-88/00060, by Schering in EP-A-186616, by Widder et al. in AJR148:399-404 (1987), by Hemmingsson et al. in Acta Radiologica 28:703-705(1987), by Hahn et al. in Society of Magnetic Resonance in Medicine, 7thAnnual Meeting, 1988, Book of Abstracts, page 738, by Saini et al. inRadiology 162:211-216 (1987), by Clement et al. in CMR89. MR20 (1989),etc.

Superparamagnetic particles free and carrier-bound are widely availableand their preparation is described in a large variety of references,e.g. WO-A-83/03920 (Ugelstad), WO-A-89/03675 (Schroder), WO-A-83/03426(Schroder), WO-A-88/06632 (Josephson), U.S. Pat. No. 4,675,173,DE-A-3508000, U.S. Pat. No. 4,827,945, U.S. Pat. No. 4,951,675 andWO-A-88/00060.

The literature thus contains many suggestions for the formulation ofsuperparamagnetic particles and in particular suggests that theparticles can be administered either free (i.e. uncoated and not boundto any other substance) or coated (e.g. dextran coated--see for exampleU.S. Pat. No. 4,452,773) or carried by or embedded in a matrix particle(e.g. a polysaccharide--see for example WO-A-83/03920 and WO-A-85/02772)or bound to an organ or tissue targetting species, e.g. a biomoleculesuch as an antibody or a hormone (see for example WO-A-88/00060 andWO-A-88/06632).

Due to the sensitivity of SQUIDS, which should be able to detect verysmall numbers of or even single superparamagnetic crystal loaded matrixparticles, tumour imaging or detection using antibody-coupledsuperparamagnetic particles may be of significant practical interest.

For such tumour imaging or detection, one may conveniently usesuperparamagnetic crystal loaded matrix particles where the matrix iscoupled to an antibody, or coated, e.g. silanized, superparamagneticcrystals where the coating is coupled to an antibody, or evenparamagnetic polychelates coupled to an antibody, preferably ones inwhich the chelated paramagnetic ions are high spin lanthanides such asDy(III), Ho(III) and Er(III). Paramagnetic polychelates have receivedmuch attention recently as potential X-ray and MRI contrast agents andare discussed for example in WO-A-90/12050.

Parenterally administrable particulate MD agents are also of particularinterest in the imaging of the liver and spleen due to the action of thereticuloendothelial system in removing such particles from the bloodstream. However MD agents and especially particulate agents may also beused to advantage in the magnetometric diagnosis or imaging of bodyducts and cavities having external voidance ducts, e.g. thegastrointestinal tract, the bladder and the uterus, where the MD agentcan be administered orally, rectally or through a catheter into the bodycavity of interest.

Many different ways of achieving tissue and organ specificity forsoluble and particulate diagnostic agents are already known.

Thus by attachment to fatty acids and other substances with a specifichydrophilic/hydrophobic ratio the agent will after intravenous injectionefficiently accumulate in the hepatocytes. Hepatocytes also havespecific lectins present on their surface. The latter causes specificoligosaccharides and glycoproteins to accumulate in the hepatocytecompartment of the liver. The Kupffer cells as well as the endothelialcells of the liver also possess unique lectins on their surface, causingother types of glycoproteins to accumulate in these compartments. Theendothelial cells of the liver have receptors for specific moleculessuch as hyaluronic acid, enabling other types of targeting vehicles alsoto be used for this compartment.

It is possible to bind the MD agent to monoclonal antibodies specificfor almost any macromolecular structure. Different organs have cellscontaining organ-specific structures on their surface. Using monoclonalantibodies reacting with organ-specific structure, it is thus possibleto produce organ-specific vehicles.

Furthermore, hormones, growth factors and lymphokines often haveorgan-specific receptors. Consequently, "natural" human proteins of thistype may also be used as targeting vehicles.

These types of targeting vehicles will cause accumulation in normalorgans, and if these are deformed and non-homogeneous due to disease, MDagents attached to such vehicles will provide important diagnosticinformation. However, for direct disease visualization, targetingvehicles with affinity for disease-specific structures should beemployed.

Thus tumour cells possess unique surface markers, and monoclonalantibodies reacting with a number of such structures have beendeveloped. Tumor-specific monoclonal antibodies coupled to MD agents canthus be used to obtain disease information, e.g. by visualization.

Thrombi contain a number of specific structures, for instance fibrin.Consequently, MD agents coupled to fibrin-specific antibodies will afterintravenous injection accumulate in the clots, and can be used fordiagnosis of the thrombi.

In the same way as Mabs with affinity for clots can be developed, thenaturally occurring protein tPA has affinity for fibrin. tPA coupled MDagents would thus accumulate in thrombi and be useful for theirdetection.

Upon cell necrosis, intracellular structures like myocine and histonesare exposed to macromolecules normally confined to the extracellularspace. Coupled to MD agents Mabs against both the above structures maythus be used to visualise infarcts/necrosis.

Where superparamagnetic particle containing contrast media areadministered parenterally, and especially intravascularly, thebiodegradation and ultimate excretion of the particle metabolites may beenhanced by formulating the particles together with a chelating agent asdescribed in WO-A-89/11873.

The superparamagnetic particles themselves may be of any material which,although preferably non-radioactive (unless the particles are alsointended to be detected by their radioactive decay emissions), exhibitssuperparamagnetism in domain and sub-domain sized crystals. Convenientlythe particles will be of a magnetic metal or alloy, e.g. of pure iron,but more preferably they will be of a magnetic iron oxide, e.g.magnetite or a ferrite such as cobalt, nickel or manganese ferrites.

For use as MD agents or tracers particular mention may also be made ofthe paramagnetic metal complexes, especially chelate complexes, whichhave been proposed for use as MRI or X-ray contrast agents.

For paramagnetic metals to be administered at effective but non-toxicdoses, they will generally be administered in the form of ionic or morepreferably, especially at higher dosage levels, non-ionic complexes,especially chelate complexes optionally bound to larger carrier ortargeting molecules which may be selected to achieve a particularbiodistribution of the MD agent--e.g. to produce a blood pooling ortissue- or organ-targeting agent--or to reduce the osmolality of the MDmedium by increasing the number of paramagnetic centres per MD agentmolecule (or molecular ion).

A wide range of suitable chelants, polychelants, and macromolecule-boundchelants for paramagnetic metal ions has been proposed in the patentliterature over the last decade and in this respect particular regardmay be had to U.S. Pat. No. 4,687,659 (Quay), U.S. Pat. No. 4,647,447(Gries), U.S. Pat. No. 4,639,365 (Sherry), EP-A-186947 (Nycomed),EP-A-299795 (Nycomed), WO-A-89/06979 (Nycomed), EP-A-331616 (Schering),EP-A-292689 (Squibb), EP-A-232751 (Squibb), EP-A-230893 (Bracco),EP-A-255471 (Schering), EP-A-277088 (Schering), EP-A-287465 (Guerbet),WO-A-85/05554 (Amersham) and the documents referred to therein, thedisclosures of all of which are incorporated herein by reference.

Particularly suitable chelants for the formation of paramagnetic metalchelate MD agents for use in the method and process of the presentinvention include the following:

N,N,N',N",N"-diethylenetriaminepentaacetic acid (DTPA),6-carboxymethyl-3,9-bis(methylcarbamoyl-methyl)-3,6,9-triazaundecanedioicacid (DTPA-BMA),

6-carboxymethyl-3,9-bis(morpholinocarbonylmethyl)-3,6,9-triazaundecanedioicacid (DTPA-BMO),

1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA),

1,4,7,10-tetraazacyclododecane-N,N',N"-triacetic acid (DO3A),

1-(2-hydroxypropyl)-1,4,7,10-tetraaza-N,N',N"-triacetic acid (HP-D03A),

1-oxa-4,7,10- triazacyclododecane-N,N',N"-triacetic acid (DOXA),polylysine-bound DTPA and DTPA derivatives and D03A and D03A derivatives(e.g. DTPA-polylysine and D03A-polylysine), dextran-bound DTPA and DTPAderivatives (DTPA-dextran) especially soluble materials which, having atotal molecular weight≧40 KD, preferably in the range 60-100 KD, areeffective as blood pooling agents.

Particularly suitable paramagnetic metal ions for chelation by suchchelates are ions of metals of atomic numbers 21 to 29, 42, 44 and 57 to71, especially 57 to 71, more especially Cr, V, Mn, Fe, Co, Pr, Nd, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, in particular Cr(III), Cr(II), V(II),Mn(III), Mn(II), Fe(III), Fe(II) and Co(II), more especially Gd(III),Tb(III), Dy(III), Ho(III), Er(III), Tm(III) and Yb(III), moreparticularly Dy(III), Ho(III) and Er(III).

In order to perform the methods of the invention with as high aspossible a safety factor (the ratio between the dose of the MD agent andits LD₅₀), it is particularly preferred to use non-ionic or lowosmolality chelates, i.e. chelates which carry no overall ionic charge,such as DyDTPA-BMA for example, or in which the complex has an overallionic charge to paramagnetic metal centre ratio of 1.5 or less.

Furthermore, where it is desired that the MD agent should remain whollyor essentially within a body duct, e.g. the blood vessels, duringpassage through the body region of interest, the MD agent willpreferably be particulate, hydrophilic or blood-pooling.

Examples of suitable blood-pooling agents include the inert solublemacromolecule-bound chelates of the type described by Nycomed inEP-A-186947 and WO-A-89/06979. Binding the chelant to a macromolecule,e.g. a polysaccharide such as dextran or derivatives thereof, to producea soluble macromolecular chelant having a molecular weight above thekidney threshold, about 40 KD, ensures relatively long term retention ofthe contrast agent within the cardiovascular system.

Examples of suitable hydrophilic MD agents include linear, branched ormacrocyclic polyaminopolycarboxylic acid chelates of paramagnetic metalions, and also especially include chelates of chelants in which one ormore carboxylic acid groupings are replaced by other groups such asamides, esters or hydroxamates, as well as such chelants in which thechelant backbone is substituted by hydrophilic groupings such as forexample hydroxyalkyl or alkoxyalkyl groups. Chelants of these types aredisclosed for example in U.S. Pat. No. 4,687,658 (Quay), U.S. Pat. No.4,687,659 (Quay), EP-A-299795 (Nycomed) and EP-A-130934 (Schering).

Particular mention however must be made of the Gd(III), Dy(III), Ho(III)and Er(III) chelates of DTPA-BMA, DTPA-BMO, HP-D03A and DO3A.

Physiologically tolerable paramagnetic porphyrin complexes, especiallycomplexes of Mn(III) and less preferably of Gd(III) or Dy(III), may alsobe used according to the invention with particular effect, e.g. intumour localization. Such porphyrin complexes are described, forexample, by Lyon et al. in Magnetic Resonance in Medicine 4:24-33(1987), by Chen et al. in FEBS 1274 168:70 (1984) and in U.S. Pat. No.4,783,529 (Lavelie). Particular mention may be made of hematoporphyrin,preferably complexed to Mn(III) but which may also be used withcobalt-58, Zinc-65 and palladium-109 as described by Bohdiewicz et al.Invest. Radiology 25:765-770 (1990). Porphyrins such astetrakis(4-sulfonatophenyl)porphyrin (TPPS) andtetrakis(N-methyl-4-pyridyl)porphyrin (TMPyP) are already known as MRIcontrast agents and are described in the literature (see for exampleHelpern et al. in Magnetic Resonance in Medicine 5:302-305 (1987),Patronas et al. in Cancer Treatment Reports 70 No. 3 p391 (1986), Fielet al. in Magnetic Resonance Imaging 5:149-156 (1987) and Chen et al.supra). To accommodate a larger metal ion (e.g. Gd (III)) a so-called"expanded porphyrin" (texaphyrin) as described in WO-A-90/10633(Univeristy of Texas), J. Am. Chen. Soc. 110:5586-5588 (1988) (Sessleret al.) and Inorganic Chemistry 28:3390-3393 (1989) (Sessler et al.) maybe used according to the invention.

Moreover, magnifier paramagnetic complexes, optionally bound totargetting biomolecules or macromolecules such as those described inWO-A-90/12050 may also be used to particular effect.

The dosages of the MD agent used according to the method of the presentinvention will vary according to the precise nature of the MD agentused, of the magnetometer being used and of the tissue or organ ofinterest. Preferably however the dosage should be kept as low aspossible while still achieving a detectable variation in magneticsusceptibility.

In general, the MD agents used according to the invention should beadministered in a quantity sufficient to produce a concentration,expressed in terms of susceptibility of at least 10⁻⁹ emu/g, preferablyat least 5×10⁻⁹ emu/g, especially at least 10⁻⁸ emu/g.

Thus viewed from a further aspect the invention provides a magneticsusceptibility MD medium in aqueous form containing a physiologicallytolerable paramagnetic or superparamagnetic substance together with atleast one pharmaceutical carrier or excipient, the magneticsusceptibility of said medium (at STP) being in the range 10⁻¹² to 10⁻⁶,preferably 10⁻¹¹ to 2×10⁻⁷, especially preferably 10⁻¹⁰ to 5×10⁻⁸, inparticular 10⁻⁹ to 10⁻⁸, emu/g.

Alternatively expressed, for most paramagnetic and superparamgneticmaterials the novel MD media will conveniently contain the magneticmetal at a concentration of at least 10⁻¹⁴ M, generally at least 10⁻¹⁰M, preferably at least 10⁻⁸ M, in particular at least 0.05 mM,especially at least 0.2 mM, more preferably at least 0.3 mM, mostpreferably at least 1.0 mM, e.g. 0.0002 to 2M, more especially 0.0003 to1.5M.

The MD media of the invention may contain particularly lowconcentrations of the contrast agent where it is a highly specificallytargeted material. Thus for an agent specific for small tumours minimumdosages of the order of 10⁻¹⁴ M/Kg may be adequate, for liver specificagents minimum dosages may be of the order of 10⁻¹¹ M/Kg and for agentswhich distribute broadly within the body minimum dosages of 10⁻¹⁰ M/kgmay be appropriate. These will generally be administered in volumes of0.1 ml to 1000 ml. The upper limit for MD agent dosages will begenerally comparable to that for MRI contrast agents and may be dictatedby toxicity constraints.

For most MD agents the appropriate dosage will generally lie in therange 0.02 μmol to 3 mmol paramagnetic metal/kg bodyweight, especially 1μmol to 1.5 mmol/kg, particularly 0.01 to 0.5, and more especially 0.1to 0.4 mmol/kg.

Where less sensitive non-SQUID magnetometers are used according to theinvention, the MD agent concentrations required will of course be higherthan are needed using SQUID magnetometers.

It is well within the skill of the average practitioner in this field todetermine the optimum dosage for any particular MD agent by simpleexperiment, either in vivo or in vitro.

Where the MD agent is ionic, such as is the case with DyDTPA, it willconveniently be used in the form of a salt with a physiologicallyacceptable counterion, for example an ammonium, substituted ammonium,alkali metal or alkaline earth metal cation or an anion deriving from aninorganic or organic acid. In this regard, meglumine salts areparticularly preferred.

MD agents may be formulated with conventional pharmaceutical orveterinary aids, for example, stabilizers, antioxidants, osmolalityadjusting agents, buffers, pH adjusting agents, etc., and may be in aform suitable for enteral or parenteral administration, e.g. oral,rectal, intravascular etc. Particularly preferably the MD agents will bein forms suitable for ingestion, injection or infusion directly or afterdispersion in or dilution with a physiologically acceptable carriermedium, e.g. water for injections. Thus the contrast agents may beformulated in conventional administration forms such as powders,solutions, suspensions, dispersions etc., however solutions, suspensionsand dispersions in physiologically acceptable carrier media willgenerally be preferred.

The MD agents may therefore be formulated for administration usingphysiologically acceptable carriers or excipients in a manner fullywithin the skill of the art. For example, the MD agents optionally withthe addition of pharmaceutically acceptable excipients, may be suspendedor dissolved in an aqueous medium, with the resulting solution orsuspension then being sterilized. Suitable additives include, forexample, physiologically biocompatible buffers chelating agents (as forexample DTPA or DTPA-bisamide (e.g.6-carboxymethyl-3,9-bis(methylcarbamoylmethyl)-3,6,9-triazaundecanedioic acid)) or calcium chelate complexes(as for example salt forms of the calcium DTPA complex or the calciumDTPA-bisamide complex, such as NaCaDTPA-bisamide) or, optionally,additions (e.g. 1 to 50 mole percent) of calcium or sodium salts (forexample, calcium chlorie, calcium ascorbate, calcium gluconate orcalcium lactate and the like).

Parenterally administerable forms, e.g., intravenous solutions, shouldof course be sterile and free from physiologically unacceptable agents,and should have low osmolality to minimize irritation or other adverseeffects upon administration and thus the MD medium should preferably beisotonic or slightly hypertonic. Suitable vehicles include aqueousvehicles customarily used for administering parenteral solutions such asSodium Chloride Injection, Ringer's Injection, Dextrose Injection,Dextrose and Sodium Chloride Injection, Lactated Ringer's Injection andother solutions such as are described in Remington's PharmaceuticalSciences, 15th ed., Easton: Mack Publishing Co., pp. 1405-1412 and1461-1487 (1975) and The National Formulary XIV, 14th ed. WashingtonAmerican Pharmaceutical Association (1975). The solutions can containpreservatives, antimicrobial agents, buffers and antioxidantsconventionally used for parenteral solutions, excipients and otheradditives which are compatible with the MD agents and which will notinterfere with the manufacture, storage or use of the products.

It will be realized of course that since the MRI contrast media can beused as MD media it will be particularly convenient to investigate thesubject using MRI to supplement or confirm diagnostic informationderived from the magnetometer investigations. Moreover, images from MRIon other conventional imaging modalities may be used to provide a"native" image onto which the magnetometric information or image may besuperimposed--this is of particular value where the biodistribution ofthe magnetometric contrast agent is very limited.

The invention will now be illustrated further with reference to thefollowing non-limiting Examples.

EXAMPLE 1

Intravenous superparamagnetic MD agent for liver, spleen and perfusionstudies (Dextran-coated superparamagnetic particles)

Dextran-coated superparamagnetic particles are prepared from FeCl₂,FeCl₃ and dextran according to Example 7.1 in WO-A-88/00060 (AdvancedMagnetics). Average particle size: 140 nm

An injectable dispersion is prepared which contains: Dextran-coatedsuperparamagnetic particles 20 mg Saline solution (0.9% sodium chloride)ad 10 ml.

The superparamagnetic particles are dispersed in saline solution andfilled into 10 ml vials under aseptic conditions. The suspension issonicated before administration to ensure complete dispersion of theparticles.

EXAMPLE 2

Intravenous superparamagnetic MD agent for tumour studies (Monoclonalantibody-coated magnetite particles)

Monoclonal antibody-coated superparamagnetic particles are preparedaccording to the method of S. Cerdan et al., Magnetic Resonance inMedicine 12:151-163 (1989).

The antibody is 33B31 (an antibody to IL-2 available from Immunotech),PP1 (an antibody to sarcoma available from Fodstad, Norwegian RadiumHospital, Oslo), or S4H9 (an antibody to the D2 fragment of fibrinogenavailable from Nycomed AS).

A dispersion of the particles is filled into 20 ml vials and freezedried. Each vial contains 48 mg Fe.

The product is dispersed in 10 ml saline before administration.

EXAMPLE 3

Intravenous paramagnetic MD agent for tumour studies (Monoclonalantibody labelled with stable free radicals)

2,2,5,5-tetramethyl-3-aminopyrrolidone-1-oxide radical is coupled tomonoclonal antibody according to the methods described in U.S. Pat. No.3,453,288.

The antibody is as in Example 2.

A solution of the labelled antibody is filled into 10 ml vials andfreeze dried. Each vial contains 0.5 mmol nitroxide radicals.

The product is dissolved in 5 ml saline before use.

EXAMPLE 4

Intravenous paramagnetic MD agent for perfusion studies (Dextran70-beta-alanine-DOTA-Dy)

Dextran 70-beta-alanine-DOTA-Dy is prepared according to Example 6 inEP-A-326226 (Nycomed).

An injectable solution is prepared which contains:

    ______________________________________                                        Dextran 70-beta-alanine-DOTA-Dy                                                                       2320   mg                                             Saline solution         ad 10  ml.                                            ______________________________________                                    

Dextran 70-beta-alanine-DOTA-Dy is dissolved in saline solution andfilled into 10 ml vials under aseptic conditions. The solution contains0.14 mmol Dy/ml.

EXAMPLE 5

Intravenous paramagnetic MD agent (Dy(III)-DO3A)

Dysprosium(III)(1,4,7-triscarboxymethyl-1,4,7,10-tetra azacyclododecane(Dy(III)-DO3A) is prepared according to Example 10 in EP-A-232751.

An injectable solution is prepared which contains:

    ______________________________________                                        Dy(III)-DO3A         2      mmol                                              Water for injections ad 20  ml                                                ______________________________________                                    

Dy(III)-DO3A is dissolved in water for injection, filled into 20 mlvials and sterilized by heating.

EXAMPLE 6

Intravenous paramagnetic MD agent (Gd(III)-DTPA)

Gadolinium(III)-diethylenetriamine-N,N,N',N",N"-pentaacetic aciddi-N-methylglucamine salt (Gd(III)-DTPA) was prepared according toExample 5 in U.S. Pat. No. 4,647,447 (Schering).

An injectable solution is prepared which contains:

    ______________________________________                                        Gd(III)-DTPA dimeglumine                                                                             10     mmol                                            CaNa.sub.3 -DTPA       0.1    mmol                                            Water for injections   ad 20  ml                                              ______________________________________                                    

Gd(III)-DTPA dimeglumine and CaNa₃ DTPA are dissolved in water forinjections, filled into 20 ml vials and sterilized by heating.

EXAMPLE 7

Intravenous MD agent (Liposome formulation of Dy(III)-DTPA)

Dysprosium(III)-diethylenetriamine-N,N,N',N",N"-pent aacetic aciddi-N-methylglucamine salt (Dy(III)-DTPA dimeglumine) is preparedaccording to Example 5 in U.S. Pat. No. 4,647,447 (Schering).

Dy(III)-DTPA dimeglumine is encapsulated into small unilamellar vesiclesaccording to the method described in EP-A-160552 (Vestar).

The purified liposome dispersion is filled into 50 ml vials and freezedried. Each vial contains 0.5 mmol dysprosium.

The product is suspended in 20 ml saline before administration.

EXAMPLE 8

Intravenous paramagnetic MD agent for tumour studies (Monoclonalantibody labelled with dysprosium)

Diethylenetriamine-N,N,N', N", N"-pentaacetic acid is coupled tomonoclonal antibodies according to the method described by D J Hnatowichet al. in Science 220:613-615.

The antibody is as in Example 2.

1.0 mole equivalent dysprosium chloride is added during agitation, thepH-value is adjusted to 5.2 and the solution is agitated for 1 hour.

The solution is dialyzed against saline for 2 days then dialyzed againstdistilled water. The aqueous solution is filled into 5 ml vials andlyophilized. Each vial contains 1 mmol dysprosium.

The product is dissolved in 5 ml or for lower concentrations 500 mlsaline before use, in the latter case only 5 ml being injected.

EXAMPLE 9

Oral superparamagnetic MD agent for abdominal studies

Particles of a sulphonated styrene-divinylbenzene copolymer matrix 3micrometers in size and themselves carrying superparamagnetic particlesto a total iron content of 19.4% by weight are prepared by the methodsof WO-A-83/03920 (SINTEF)

A suspension for oral administration is prepared which contains:

    ______________________________________                                        Superparamagnetic particles                                                                           0.1 g                                                 Hydroxyethyl cellulose  8.0 g                                                 Methyl parahydroxybenzoate                                                                            0.7 g                                                 Propyl parahydroxybenzoate                                                                            0.15 g                                                Ethanol                 10.0 g                                                Saccharin sodium        1.0 g                                                 Anis essence            0.2 g                                                 Water                   ad 800 g                                              ______________________________________                                    

Hydroxyethyl cellulose is dispersed in water with stirring for 2 hours.Saccharin sodium and a solution of anis essence, methyl and propylprahydroxybenzoate in ethanol are slowly added. The superparamagneticparticles are dispersed in the solution under vigorous stirring.

The suspension is filled into a 800 ml bottle. The suspension contains19.4 mg iron.

EXAMPLE 10-11

Multi-channel SQUID analysis of 0.5% agar gels containing MD agents.

SQUID Instrument: Krenikon (SIMENS AG)

All samples were moved with the same frequency (appr. 4 Hz) during theexperiments.

SQUID signals (16 channels) without sample is shown in FIG. 1.

EXAMPLE 10

MD agent: Superparamagnetic starch microspheres prepared according to(Schroder and Salford)

Concentration: 0.1 mmol/kg

Distance from detector: 1 cm

Results shown in FIG. 2.

EXAMPLE 11

MD agent: GdDTPA-BMA prepared according to U.S. Pat. No. 4,687,658(Quay)

Concentration: 0.1 mmol/kg

Distance from detector: 1 cm

Results shown in FIG. 3.

EXAMPLE 12-13

Multi-channel SQUID analysis of the same samples as described in Example10-11 after magnetization of the samples with a small, strong (about 0.3T) permanent magnet showed enhanced magnetometric effect compared to thenon-magetized samples.

(No corrections have been made for potential magnetization of the emptyplastic test tubes).

EXAMPLES 14-15

SQUID analysises of the samples in Examples 19-26 are performed on aninstrument detecting magnetic fields. Enhanced efficiency is observed.

(The instrument used in Examples 10-13 detects magnetic field gradientsand not the absolute magnetic fields).

EXAMPLES 16 to 22

Low concentration intravenous MD media

The MD media of Examples 1 to 7 are diluted, 1 part by volume with 99parts by volume of water for injections to produce more dilute contrastmedia suitable for use with sensitive SQUID based magnetometers.

Still lower concentrations, e.g. at the 10⁻¹⁰ -10⁻⁶ M level, can beproduced by further dilution.

We claim:
 1. A method of generating a magnetometric image of the human or non-human animal body comprising administering to said body a physiologically tolerable superparamagnetic material and generating a magnetometric signal of at least part of said body into which said material distributes.
 2. A method as claimed in claim 1, wherein said signal is a magnetometric image of at least part of said body into which said material distributes.
 3. A method as claimed in claim 2, wherein said image generated is a two or three dimensional structural image.
 4. A method as claimed in claim 1, wherein said signal is generated using a superconducting quantum interference device (SQUID) magnetometer.
 5. A method as claimed in claim 4, wherein said signal is generated using a multichannel SQUID system.
 6. The method as claimed in claim 1, wherein a superparamagnetic material is used as a magnetometric diagnostic (MD) agent with no pre-magnetization thereof and no magnetic field or with a static magnetic field being imposed during signal generation.
 7. A process for detecting variations in magnetic susceptibility within a human or non-human animal body, comprising administering to said body a physiologically tolerable superparamagnetic material, and with a magnetometer continuously or repeatedly monitoring the magnetic susceptibility of at least a part of said body into which said material distributes.
 8. A process as claimed in claim 7 comprising generating a magnetometric image.
 9. A process as claimed in claim 7, wherein said magnetometer is a superconducting quantum interference device (SQUID) magnetometer.
 10. A process as claimed in claim 9, wherein said magnetometer is a multichannel SQUID system.
 11. The process as claimed in claim 7, wherein a superparamagnetic material is used as a magnetometric diagnostic (MD) agent with no pre-magnetization thereof and no magnetic field or with a static magnetic field being imposed during signal generation. 